Don't crash when Database::DoesColumnExist is called on a poisoned DB

Many functions in sql::Database, in particular Database::DoesTableExist,
handle a poisoned DB gracefully and return false in case the DB is
poisoned. This CL adds similar logic to Database::DoesColumnExist.

Bug: 1432475
Change-Id: Ib4ed90abb9dc4030ccac714b1dbd2388acb1a396
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4427823
Reviewed-by: Austin Sullivan <asully@chromium.org>
Commit-Queue: Dominic Battre <battre@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1144202}

sql/database.cc

@@ -1675,6 +1675,11 @@ bool Database::DoesColumnExist(const char* table_name,
                                const char* column_name) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
+  if (!db_) {
+    DCHECK(poisoned_) << "Illegal use of Database without a db";
+    return false;
+  }
+
   // sqlite3_table_column_metadata uses out-params to return column definition
   // details, such as the column type and whether it allows NULL values. These
   // aren't needed to compute the current method's result, so we pass in nullptr